The semiconductor manufacturing industry places increased emphasis on cost savings and efficiency to increase a constantly dwindling profit margin. One important effort to drive costs lower is to preserve components within a system that requires extremely high ion energy at the substrate surface when using helium based plasma to complete the required etching process. To create this high ion energy at the substrate surface, a high voltage is applied at the substrate surface, which creates a large electrical field gradient extending back into the helium supply line, which in turn creates unwanted electrical arcing between surfaces and generates plasma in the supply lines and other components. This produces adverse effects such as pitting and melting of the supply lines. Disposing an electrical insulator between the area of high electrical potential and the supply lines can minimize impact of unwanted electrical arcing and plasma generation. However, such electrical insulators increase cost of ownership. Great care must be taken to avoid the unnecessary wear rate of system parts.
FIG. 1 is a cross-sectional view of a conventional helium supply system 100 of a chamber wafer processing system 112. System 100 includes a flexible helium supply line 102, a metallic weldment 104, a dielectric arrestor insert 106, a dielectric arrestor housing 108, an ESC mounting plate 118, and a bowl housing assembly 116. Arrestor housing 108 is shaped to include a cylindrical cavity 120 for holding dielectric arrestor insert 106. Flexible helium supply line 102, metallic weldment 104, dielectric arrestor insert 106, arrestor housing 108, and ESC mounting plate 118 reside in bowl housing assembly 116. Chamber wafer processing system 112 includes an electro-static chuck (ESC) 110 that is operable to electrostatically hold a wafer for processing.
In operation, helium is supplied to chamber wafer processing system 112 via conventional helium supply system 100. The path of the helium through conventional helium supply system 100 as indicated by arrows within flexible helium supply line 102, metallic weldment 104 and arrows 114 through dielectric arrestor insert 106.
Operation of the ESC requires the use of high voltage DC power be applied to clamp the wafer, and high-frequency RF power to generate the plasma needed for wafer processing. Helium is supplied to the ESC to effect thermal sinking between the wafer and the ESC 110. Application of either the high voltage DC or RF power can, in turn, excite the helium to a point where electrons are able to escape the bond of the helium atom, thus generating plasma. The time at which gaseous helium is converted into plasma is commonly referred to as “light-up.”
Mounting plate 118, which is usually operated at a high voltage potential similar to what that of ESC 110, is electrically-separated from flexible helium supply line 102 and metallic weldment 104, by arrestor housing 108, and dielectric arrestor insert 106. Bowl housing assembly 116 is at ground potential. It is desirable that flexible helium supply line 102 and metallic weldment 104 be shielded from the electrical and magnetic field effects from ESC 110. Further, the electrical potential of metallic weldment 104 and flexible helium supply line 102 should closely match that of bowl housing assembly 116 to prevent electrical arcing between the two, or to prevent a high voltage potential between the two so as to cause light-up within flexible helium supply line 102. If electrical arcing occurs, damage to bowl components can occur. If plasma light-up occurs, pitting and melting of the supply lines and other components within bowl housing assembly 116 can occur. The requirement to hold metallic weldment 104 at the ground potential of bowl 116 results in a large voltage potential impressed across arrestor housing 108, and dielectric arrestor insert 106.
At lower helium pressures between 1 to 50 Ton (pressures between 1/760 and 50/760 of standard atmospheric pressure), which is typical of normal operating conditions of chamber wafer processing system 112 and system 100; the helium can conduct electrical current and generate electrical arcing under certain conditions. The likelihood of plasma generation or arcing within arrestor housing 108 and dielectric arrestor insert 106 is directly related to the voltage potential difference, and inversely related to the gas path length, between metallic weldment 104 and mounting plate 118, and is also directly related to the cross-section mean free path available, which will be discussed in more detail below.
FIG. 2A is an oblique view of dielectric arrestor insert 106. Dielectric arrestor insert 106 includes a first cylindrical portion 202, spaced from a second cylindrical portion 204 via a circumferential channel 206. First cylindrical portion 202 has a circular face 208, whereas second cylindrical portion 204 has a circular face 210. Circular face 208 has a helium entry 216, whereas circular face 210 has a helium exit 218. A longitudinal channel 212, having a width d1 and a depth d2, extends from helium entry 216 at circular face 210 to circumferential channel 206, whereas a longitudinal channel 214 extends from circumferential channel 206 to helium exit 218.
FIG. 2B is a cross-sectional view of dielectric arrestor insert 106. In the figure, helium gas flows along a path indicated by arrows 114. Specifically, helium provided by metallic weldment 104 enters helium entry 216, proceeds through longitudinal channel 212, proceeds around circumferential channel 206, continues through longitudinal channel 214 and finally exits out helium exit 218 into chamber wafer processing system 112. The total distance that the helium gas travels in dielectric arrestor insert 106 includes the length of longitudinal channel 212, half the circumference of circumferential channel 206 and the length of longitudinal channel 214.
Returning back to FIG. 1, dielectric arrestor insert 106 is tightly disposed within cylindrical cavity 120 of arrestor housing 108. Accordingly, cylindrical cavity 120 closes longitudinal channel 212, circumferential channel 206 and longitudinal channel 214 to form tubes such that helium gas will only pass through longitudinal channel 212, circumferential channel 206 and longitudinal channel 214. Dielectric arrestor insert 106 provides an insulator block between a low electrical potential of metallic weldment 104 and a high potential of mounting plate 118. Metallic weldment 104 is at or near ground potential and mounting plate 118 is at a high electrical potential. Because of the voltage difference between metallic weldment 104 and mounting plate 118, there is a possibility of light up and arcing of helium within dielectric arrestor insert 106 or arrestor housing 108. At least one of two tactics may be employed to reduce the potential of arcing or light-up in dielectric arrestor insert 106 or arrestor housing 108.
First, width d1 and depth d2 of longitudinal channel 212 of dielectric arrestor insert 106 can be decreased. For a constant supply of helium, decreasing width d1 and depth d2 of longitudinal channel 212 of dielectric arrestor insert 106 will reduce the cross-sectional area and thus reduce the space for electrons to move in an excited state to produce plasma. A problem with this tactic is that decreasing the width d1 and depth d2 of longitudinal channel 212 of dielectric arrestor insert 106 will increase the pressure drop across the components, and that will decrease the amount of helium supplied into wafer processing system 112.
Second, the total length that the helium gas travels in dielectric arrestor insert 106 can be increased. This will effectively increase the distance between metallic weldment 104 and ESC 110 as viewed from an electrostatic field induced through helium within longitudinal channel 212, circumferential channel 206 and longitudinal channel 214. This will reduce the voltage gradient over the total length that the helium gas travels in dielectric arrestor insert 106 making dielectric arrestor insert 106 a better insulator block. However, arcing or light-up potential can be an issue if the increased length comes in the form of a longer, line-of-site path. Also, there is only a limited amount of space in arrestor housing 108 and bowl housing assembly 116. As such, in system 100, this is not a viable option.
Finally, the dielectric constant of the electrically insulative material may be decreased.
The dielectric arrestor insert 106 includes a width d1 and depth d2 of longitudinal channel 212 that is sufficiently large to provide sufficient helium into wafer processing system 112. Further, as noted above, the total length that the helium gas travels in dielectric arrestor insert 106 includes the space in arrestor housing 108. The width d1 and depth d2 of longitudinal channel 212 in combination with a short total length that the helium gas travels in dielectric arrestor insert 106 affect the ability of dielectric arrestor insert 106 to prevent arcing and plasma generation in dielectric arrestor insert 106 itself.
What is needed is a dielectric arrestor insert that decreases the likelihood of arcing and plasma generation in the dielectric arrestor insert itself, while not causing and adverse pressure drop.